1. Field of the Invention
The present invention relates to a compatible optical pickup device which can compatibly read/write optical disks of the CD family or DVD family, and more particularly, to a compatible optical pickup device using a single light source to emit light having a wavelength longer than 650 nm.
2. Description of the Related Art
A typical optical pickup device reproduces and records information on and/or from a recording medium in a non-contact manner. An optical pickup device capable of performing reproducing/recording of optical disks of the DVD family having a thickness of 0.6 mm (hereinafter referred to as “DVD”) uses an objective lens having a numerical aperture of 0.6 and a light source to emit light having a 650 nm wavelength. Here, the optical pickup device for DVD should be compatible with optical disks of a CD family which is 1.2 mm thick (hereinafter referred to as “CD”).
In consideration of the above matter, optical pickup devices which can compatibly reproduce/record optical disks in different formats have been suggested. A conventional optical pickup which can compatibly reproduce/record a CD and a DVD is shown in FIG. 1 and has the structure using two light sources 1 and 3 to emit light having different wavelengths.
Referring to FIG. 1, a first light source 1 emits light having 635 or 650 nm to reproduce/record a DVD 10a, which is relatively thin. A second light source 3 emits light having a 780 nm wavelength to reproduce/record a CD 10b, which is relatively thick. A grating 5 diffracts and splits light output from the second light source 3 into the 0th order and the ±1st order rays to detect a tracking error signal by a three-beam method during reproducing/recording of the CD 10b. The light emitted from the first light source 1 passes through a first beam splitter 7 and is reflected by a second beam splitter 9 so as to proceed toward the DVD 10a. The light emitted from the second light source 3 is sequentially reflected by the first and second beam splitters 7 and 9 and proceeds toward the CD 10b. A collimating lens 11 converts the divergent light output from the first and second light sources 1 and 3 into a parallel beam. An objective lens 15 focuses incident light output from the first and second light sources 1 and 3 to form a light spot. Here, the light emitted from the first light source 1 is focused on the relatively thin DVD 10a while the light emitted from the second light source 3 is focused on the relatively thick CD 10b. 
The light reflected by an optical disk 10 is incident on the second beam splitter via the objective lens 15. Most of the light passes through the second beam splitter 9 and is received by a photodetector 19 after passing through a sending lens 17 to focus the incident light reflected by the optical disk 10.
Since the conventional compatible optical pickup device having the above structure includes two light sources 1 and 3 emitting light having different wavelengths, optical disks 10 of both the CD 10b family and the DVD 10a family can be reproduced/recorded.
However, since the conventional compatible optical pickup device uses two separate light sources, a cost of manufacturing is high and the structure thereof is complicated, and further, assembly and optical arrangement is difficult. Further, the light source 1 for a 635 nm or 650 nm wavelength which can emit recording power for DVD-R and/or DVD-RAM is expensive, which increases the entire cost of a compatible optical pickup device.